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patricia will flip the coin 8 times. let a be the event that exactly 4 of the 8 flips are heads, and b be the event that the last two flips are tails. find p(a ∪ b).

Sagot :

The probability of an event of P(A∪B) is 49/128.

In this question,

Patricia will flip the coin 8 times.

The sample space is the flipping of a coin 8 times.

⇒ n(s) = 2⁸

⇒ n(s) = 256

Let A be the event that exactly 4 of the 8 flips are heads

⇒ n(A) = [tex]8C_4[/tex]                 [∵ [tex]nC_r=\frac{n!}{r!(n-r!)}[/tex]]

⇒ [tex]\frac{8!}{4!4!}[/tex] = 70

Then, P(a) = [tex]\frac{n(a)}{n(s)}[/tex]

⇒ [tex]\frac{70}{256}[/tex]

Let B be the event that the last two flips are tails

⇒ n(B) = [tex]8C_2[/tex]

⇒ [tex]\frac{8!}{2!6!}[/tex] = 28

Then, P(a) = [tex]\frac{n(b)}{n(s)}[/tex]

⇒ [tex]\frac{28}{256}[/tex]

Now, P(A∪B) = P(A) + P(B)

⇒ P(A∪B) = [tex]\frac{70}{256} + \frac{28}{256}[/tex]

⇒ P(A∪B) = [tex]\frac{70+28}{256}[/tex]

⇒ P(A∪B) = [tex]\frac{98}{256}[/tex]

⇒ P(A∪B) = [tex]\frac{49}{128}[/tex]

Hence we can conclude that the probability of an event of P(A∪B) is 49/128.

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